This symbol represents (here) the equivalent of a probability distribution which need not sum/integrate to 1.
This symbol represents (here) the equivalent of a probability distribution which need not sum/integrate to 1, but rather to some finite positive real value (e.g. the partition function \( \htmlClass{sdt-0000000077}{Z} \)).
The symbol \( F \) is used to represent the general concept of a measure. Here, it names a probability distribution, possibly before normalization for integrating to 1: it takes non-negative values and integrates to a finite positive real value \( \htmlClass{sdt-0000000077}{Z} \).